Hydraulic brake booster

Abstract

A hydraulic brake booster for use in a brake system having a housing with a power piston located in a first bore and a control valve located in a second bore. An input member is connected to the power piston and linked to the control valve by a lever arrangement. The input member is characterized by a cylindrical body with a shaft attached thereto. A bracket with a radial opening is carried by the shaft and urged toward a head on the shaft by a spring. The lever arrangement is characterized by a first lever with a first end pivotally secured in the housing by a first pin and a second end located in the radial opening of the bracket and a second lever pivotally secured at a fulcrum on the first lever by a second pin extending through the first and second levers. A first input force applied to the cylindrical body is transmitted through the spring into the bracket and communicated through the fulcrum point to bring a first end of the second lever into engagement with the control valve and a second end of the second lever into engagement with the power piston. The first input force as applied to the bracket causes the end of the first lever to pivot about the first pin and transmit an actuation force through the fulcrum into the said second pin to move said first end and activate said control valve to meter pressurized fluid into the working chamber to develop a hydraulic force for effecting a brake application. The lever arrangement ratio defined by a first length between the first pin and the second end on the first lever and a second length between the first pin and the second end of the second lever such that axial movement of the cylindrical body and the power piston is defined by this ratio and as a result a hydraulic force produced by the metered pressurized fluid proportional to a manual input force.

We claim:  
     
       1. A hydraulic brake booster for use in a brake system having a housing with a first bore separated from a second bore, said first bore retaining a power piston and said second bore retaining a control valve, an input member connected to said power piston and linked to said control valve by a lever arrangement, said lever arrangement is responsive to a first input force that is communicated from the input member for moving said control valve to meter pressurized fluid to a working chamber in said housing, said pressurized fluid in said working chamber acting on said power piston to develop a hydraulic force to pressurize fluid in said first bore that is communicated to wheel brakes in a brake system to effect a corresponding brake application, said input member is characterized by a cylindrical body, a shaft having a head on a first end and axial slot located between said head and threads on a second end, a bracket located on said shaft, said bracket having a radial opening, and a spring located between said bracket and said cylindrical body and on said threads being mated with said cylindrical body said spring urges said bracket into engagement with said head; and wherein said lever arrangement is characterized by a first lever with a first end pivotally secured in said housing by a first pin and a second end located in said radial opening of said bracket, a second lever having a first end and a second end with said first pin passing through a slot in said first end, a second pin extending through said first and second levers to define a fulcrum point for said lever arrangement, and a second spring is located between said power piston and said head such that a return spring force is applied to said bracket and communicated through said fulcrum point to bring said first end of said second lever into engagement with said control valve and said second end of said first lever of said second lever into engagement with said power piston, said first input force being applied through said bracket to said second end of said second lever of said first lever causing said second end to pivot about said first pin and transmit an actuation force through said fulcrum into said second lever to move said first end and activate said control valve whereby metered pressurized fluid is communicated into said working chamber for effecting said brake application, said lever arrangement having a first length defined by a distance between said first pin and said second end on said first lever and a second length defined by a distance between said first pin and said second end of said second lever such that axial movement of said cylindrical body and said power piston is defined by a ratio of said first length to said second length and as a result said hydraulic force is proportional to said input force. 
     
     
       2. The brake booster as recited in  claim 1  wherein said first end of said second lever is characterized by a cam surface that engages said control valve such that as said first lever pivots on said first pin the actuation force is balanced between said control valve and said power piston. 
     
     
       3. The brake booster as recited in  claim 2  wherein said power piston is characterized by an axial projection that extends into said working chamber and said bracket is characterized by a slot that engages said projection to align said radial opening with said first lever. 
     
     
       4. The brake booster as recited in  claim 3  wherein said input member is further characterized by a third pin located that is in said axial slot of said shaft to limit the movement of said bracket with respect to said shaft. 
     
     
       5. The brake booster as recited in  claim 4  wherein said power piston is characterized by a stop pin that extends through said axial projection to limit the movement of said bracket with respect to said power piston. 
     
     
       6. The brake booster as recited in  claim 5  wherein said body cylindrical body is characterized by a lip that engages said housing to provide a stop to position said cylindrical in a rest position within said working chamber. 
     
     
       7. The brake booster as recited in  claim 6  wherein said power piston is characterized by a second axial bore that receives said second spring and said head on said shaft to assist in aligning said cylindrical body with said power piston. 
     
     
       8. The brake booster as recited in  claim 7  wherein said input member is further characterized by said shaft having a third bore therein that extends from said head to said axial slot with a seat in said third bore adjacent said head, a ball located in said third bore, a third spring for urging said ball toward said seat and a fourth pin located in said third bore that engages said third pin and said ball to hold said ball off said seat to allow fluid communication between said working chamber and said second axial bore. 
     
     
       9. The brake booster as recited in  claim 8  wherein said cylindrical body and power piston move at different rates in response to said first input force such that up to a maximum level for said pressurized fluid in said working chamber said bracket moves away from said power piston and when said maximum level is attained said first lever engages said housing to hold said bracket in a stationary position and thereafter said shaft moves with respect to said third pin to allow said fourth spring to correspondingly move said ball against said seat and close communication between said working chamber said second axial bore to define a solid link between said cylindrical body and power piston such that said first input force applied by the operator to said cylindrical body is added to the hydraulic force to effect a brake application. 
     
     
       10. The brake booster as recited in  claim 1  further characterized by a second input force being applied to said first end of said second lever to activate said control valve and meter pressurized fluid to said working chamber for developing said hydraulic force to pressurize fluid in said first bore to effect an independent brake application, and wherein said cylindrical body is characterized by a lip that engages said housing to retain said cylindrical body in said housing as a result of a force acting thereon by said pressurized fluid in said working chamber. 
     
     
       11. The brake booster as recited in  claim 10  wherein said power piston is further characterized by an axial projection that extends into said working chamber and a third pin located adjacent an end of said axial projection, and said bracket is further characterized by an axial slot that engages said projection, said bracket remaining stationary within said working chamber until said hydraulic force moves said power piston in said first bore to bring said third pin into engagement with said bracket to pressurize fluid in said first bore and to develop said independent brake application. 
     
     
       12. The brake booster as recited in  claim 11  further characterized by said engagement of said third pin with said bracket and further movement of said power piston causing said first lever to pivot on said first pin and impart an auxiliary force through said fulcrum to bring said second end of said second lever into engagement with said power piston. 
     
     
       13. The brake booster as recited in  claim 12  further characterized by an actuation chamber in said housing having a piston located therein with a projection that extends into said working chamber and engages said first end of said second lever, said actuation chamber receiving pressurized fluid that acts on said piston to develop said second input force. 
     
     
       14. The brake booster as recited in  claim 13  wherein said first end of said second lever is further characterized by a second cam surface such that auxiliary force moves said second end of said second lever into engagement with said power piston without the development of noise. 
     
     
       15. The brake booster as recited in  claim 1  further characterized by a second input force being applied to said first end of said second lever to activate said control valve and meter pressurized fluid to said working chamber for developing said hydraulic force to pressurize fluid in said first bore to effect an independent brake application, and wherein said cylindrical body is characterized by a lip that engages said housing to retain said cylindrical body in said housing as a result of a force acting thereon by said pressurized fluid in said working chamber.